B chromosomes: from cytogenetics to systems biology

Abstract

Though hundreds to thousands of reports have described the distribution of B chromosomes among diverse eukaryote groups, a comprehensive theory of their biological role has not yet clearly emerged. B chromosomes are classically understood as a sea of repetitive DNA sequences that are poor in genes and are maintained by a parasitic-drive mechanism during cell division. Recent developments in high-throughput DNA/RNA analyses have increased the resolution of B chromosome biology beyond those of classical and molecular cytogenetic methods; B chromosomes contain many transcriptionally active sequences, including genes, and can modulate the activity of autosomal genes. Furthermore, the most recent knowledge obtained from omics analyses, which is associated with a systemic view, has demonstrated that B chromosomes can influence cell biology in a complex way, possibly favoring their own maintenance and perpetuation.

Chromosomal Mapping of Repeat DNA in <b><i>Bergiaria westermanni</i></b> (Pimelodidae, Siluriformes): Localization of 45S rDNA in B Chromosomes

“…, 2005;Yoshida et al, 2011;Ruíz-Estévez et al . , 2012;BanaeiMoghaddam et al, 2015], and the presence of multigene families in these chromosomes was also reported [for a review, see Valente et al, 2017]. In addition to the presence of genes, it has been proposed that transcription factors, miRNAs, and ncRNAs, including lncRNAs, of B chromosomes can promote modifications in the expression of genes from A elements [Valente et al, 2017].…”

“…In the grasshopper Eyprepocnemis plorans , 45S rDNA sequences of B chromosomes can be active [Ruiz-Estévez et al, 2012]. Furthermore, Valente et al [2017] proposed that B chromosomes contain transcriptionally active sequences, which may modulate the gene expression in A elements.…”

B‐chrom: a database on B‐chromosomes of plants, animals and fungi

“…The presence of Bs is not associated with any phenotype in most cases (Valente et al ., ), particularly when the number of Bs is low. The maximum number of Bs tolerated is variable across species and it is counterbalanced by their potential negative consequences, particularly on fertility and vigour (Houben, ).…”

First report of B chromosomes in three neotropical thorny catfishes (Siluriformes, Doradidae)

“…However, there are exceptions, as described in Nectria haematococca Samuels & Rossman, 1999 where the Bs possess resistance genes which grant a better pathogenicity (Coleman et al 2009), and in Lithochromis rubripinnis Seehausen, 1998 in which B chromosomes have a functional effect in sex determination (Yoshida et al 2011). According to Valente et al (2016), the recent development of molecular biology associated with the advances in next-generation sequencing technologies have increased knowledge about the biological importance of B chromosomes, revealing that the presence of many genes and other transcriptionally active sequences can modulate the activity of autosomal genes.…”